JPH01220825A - Aligner - Google Patents

Abstract

PURPOSE:To reduce speckle by dividing a laser beam into two parts, rotating the one of them by 90 deg. in respect to the travelling direction, overlapping the two beams coaxially or in parallel, and constituting this beam so as to be used for illuminating an original plate. CONSTITUTION:A beam of S polarization component reflected by a polarization beam splitter 8 is reflected by mirrors 4, 5 and reflected by a polarization beam splitter 6. Then it enters an optical system 11 which uniformizes luminous intensity. A beam of P polarization component which has transmitted through a polarization beam splitter 3 is reflected by mirrors 7, 8, 9. Since the mirror 7, 8, 9 are rotated 45 deg., in a body, on an optical axis Cl, the shape of a beam reflected by the mirror 9 is rotated 90 deg., and the polarization palne also is rotated 90 deg.. Therefore by arranging a 1/2 wave length plate 10 between the mirror 9 and the beam splitter 6, a beam 15 becomes P-polarization, which is coaxially overlapped with a S polarization beam 14 and enters the optical system 11. A light flux emitted from the optical system 11 illuminates a reticle R with a uniform intensity via a reflecting mirror 12 and a condenser lens 13, and a projection lens 7 forms a pattern image on a photosensitive layer on the upper surface of a wafer W. Thereby, the image quality of a projected pattern can be equal in the longitudinal direction and the lateral direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure apparatus that transfers a pattern, and more particularly to an exposure apparatus that transfers an LS pattern onto an object using a laser light source.

[Conventional technology]

A deep UV exposure device using an excimer laser as a light source is attracting attention as a transfer device for fine LSI patterns of the 0.5 μm rule or less. In particular, a device that uses a narrow-band laser with a narrow laser oscillation wavelength width and uses a projection lens made only of quartz as an optical material to reduce and expose the pattern of an original plate such as a reticle or mask onto a photosensitive substrate such as a wafer is in the early stages. It is expected that this technology will be put into practical use.

[Problem that the invention seeks to solve]

In the above types of devices, the excimer laser light source tends to have high spatial coherence.

For example, when a master-slape type injection locking laser is used, the illumination light has a small number of oscillation modes and is highly coherent, which tends to cause transfer patterns and unnecessary interference fringes called superimposed speckles to appear on the wafer.

In addition, even with narrowband lasers that maintain a large beam diameter by inserting an etalon (two parallel quartz plates spaced apart at a regular interval) into the laser resonator to avoid reducing the number of oscillation modes, spatial coherence is still a problem. is higher than the state before narrowing, and there was a problem that the spatial coherence was high, especially in directions where the beam divergence angle was small, and unnecessary interference fringes were likely to appear.

[Means for solving problems]

In order to solve the above problems, in the present invention, a laser beam for illuminating an original set in an exposure device is divided into two, and one beam is set at an angle of approximately 90° with respect to the direction in which the beam travels.
After rotation, the two beams were superimposed substantially coaxially or substantially parallel, and the superimposed beams were configured to be used to illuminate the original.

[Effect]

In the present invention, a laser beam such as an excimer is divided into two, and one beam is rotated with respect to the other by about 90'' and superimposed, so that in a plane perpendicular to the direction of travel of the beam, two orthogonal directions are Spatial coherence can be made approximately equal.

〔Example〕

FIG. 1 is a configuration diagram of the first embodiment of the present invention, where l is a laser light source with a narrowed spectrum, and 2 is a beam expander including a cylindrical lens system, which extends the beam only in the -dimensional direction. In this embodiment, the beam width is expanded only in the y direction. The laser light source 1 is of a type in which an etalon is placed inside a resonator, and the polarization is random. 3 is a polarizing beam splitter
The polarized light component (P polarized light) whose electric field is within the plane of the paper is transmitted, and the polarized light component (S polarized light) perpendicular to the plane of the paper is reflected. 6 is a similar polarizing beam splitter. 4.5.7.8
．． 9 is a total reflection mirror.

The S-polarized component beam reflected by the polarizing beam splitter 3 is reflected by the mirror 4.57, and is sent to the polarizing beam splitter.
After being reflected at 6, the light enters the illumination intensity uniformization optical system 11. The P-polarized component beam transmitted through the polarizing beam splitter 3 is reflected by the mirror 7.8.9.
The incident-reflection surface of 8.9 is inclined at 45° with respect to the plane of the paper. That is, the mirrors 7.8.9 are rotated together by 450 degrees around the horizontal optical axis C2. Therefore, the beam shape of the beam after being reflected by mirror 9 is rotated by 90 degrees with respect to the beam before entering mirror 7.
The polarization is also rotated by 90 degrees. Therefore, the 1/2 wavelength plate 10 made of quartz or the like is connected to the mirror 9 and the polarizing beam splitter.
6, the beam 15 passing through the 1/2 wavelength plate becomes P-polarized light for the polarizing beam splitter 6, and is superimposed coaxially with the S-polarized beam 14 from the mirror 5, making it uniform. The light enters the optical system 11.

2 (A), (B), and (C) show the beam cross-sectional shape at each location of the laser beam in FIG. 1, and FIG. 2 (A) shows the beam cross-sectional shape at each location in FIG. Laser light'f! This is a cross section of the output beam immediately after ejecting A1, and it becomes wider in the -dimensional X direction. This beam has a smaller beam divergence angle in the y direction, and higher spatial coherence in the y direction than in the This is the cross-sectional shape of the laser beam after passing through Goo 2, and the beam has approximately the same width in the x and y directions, but the y
The spatial coherence in the direction is much higher than in the X direction.

FIG. 2(C) shows the cross-sectional shape of the beams after being superimposed at position C1 in FIG. 1, that is, the polarizing beam splitter 6, and the beams 14 and 15 are substantially coaxially superimposed. In this state, spatial coherence is equal in the two directions, X and y.

Next, returning to FIG. 1 and continuing the explanation of this embodiment, an illumination intensity uniformizing optical system 11 into which the superimposed beams 14 and 15 are incident includes a fly-eye lens, etc., and a scanning mirror for speckle reduction. It also includes optical systems such as Regarding the combination of this ply eye lens and scanning mirror,
Details are disclosed in Japanese Unexamined Patent Publication No. 59-226317.

The light flux emitted from the homogenizing optical system 11 passes through a reflection mirror 12 and a condenser lens 13 to illuminate the original reticle R with uniform illuminance, and the projection lens L projects an image of the pattern on the underside of the reticle onto the wafer W. It is designed to be formed on the upper photosensitive layer.

As described above, in this embodiment, the laser light source 1, beam expander 2, beam splitters 3, 6, mirrors 4.5.7
．． 8.9 and the 1/2 wavelength plate 10 constitute an illumination system for the exposure apparatus.

In the first embodiment described above, a laser light source l that emits a randomly polarized beam using an etalon is used, but next, a dispersive element with remarkable polarization characteristics such as a prism or grating is used to narrow the spectrum. A second embodiment will be described as an optimal example when using a laser light source of this type.

In the second embodiment, the output beam of the laser light source 1 is polarized in one direction. In this case, the polarizing beam splitter 3 in the first embodiment is replaced with a beam splitter that does not have polarization characteristics and makes the intensity ratio of reflected light and transmitted light 1:1, and the 1/2 wavelength plate 10 is used. Just remove it.

In the description of the first and second embodiments, the beam expander 2 is provided in front of the beam splitter 3, but it may not be provided or may be provided after the beam splitter 6.

Although the illumination intensity uniformization optical system 11 was placed after the beam splitter 6, it would be better to place an optical system for speckle reduction (scanning mirror, fly-eye lens, fiber, etc.) before the beam splitter 3. It may yield good results for reducing spatial coherence.

In addition to stripping the beam by rotating it by 90 degrees and overlapping it, for example, it is possible to divide the beam into three parts and rotate the beam by 120 degrees and 240' and then overlap it with the original non-rotated beam. Although it is unavoidable that the energy loss increases when superimposing the elements, it is effective in eliminating the directionality of spatial coherence. Therefore, dividing into three beams in this manner is also included as an embodiment of the present invention.

In the first and second embodiments described above, the polarizing beam splitter 6 was used as a method of superimposing the two divided beams again, but it is possible to use a partial reflecting mirror instead at a low cost and to change the polarization direction. This makes it possible to create an optical arrangement that does not depend on the

FIG. 3 shows the configuration of an exposure apparatus according to a third embodiment of the present invention, in which a partial mirror 20 as a superimposing means of the present invention is provided in place of the beam splinter 6 shown in FIG. The original non-rotated beam 14 reflected at right angles by the mirror 20 and the 90'' rotated beam 15 transmitted through the side of the partial mirror 20 are not coaxial with each other, but enter the homogenizing optical system 11 almost parallel to each other.Others , the configuration is the same as that of FIG. 1 except that the 1/2 wavelength plate 10 is omitted.

In the case of this embodiment, the optical axis of the projection lens L and the beam 14.1
It is eccentric to each central axis of 5.

Figure 4 (A), (B), and (C) are positions A and B in Figure 3.
, C shows the cross-sectional shape of the beam at each position A,
The cross-sectional shape at B is the same as in FIGS. 2(A) and 2(B). However, in this embodiment, as shown in FIG. 4(C), the beams 14 and 15 rotated by 90@ are approximately the width of each other in the y direction at position C immediately after the partial mirror 20 in FIG. The beams 14 and 15 are eccentric from the same axis by a certain amount, so that the beams 14 and 15 do not overlap with each other. In this embodiment, as shown in FIG.
Although the overall cross-sectional shape of the beam 14.15 incident on the beam 14.15 is not square, the beam 14.15 enters the homogenizing optical system 1.
It is also possible to provide a beam expander (cylindrical lens) in the -dimensional direction before the beams 14 and 15 enter the beams 14 and 15 (position C), thereby making the overall shape of the beams 14 and 15 nearly square again.

As described above, in the first, second, and third embodiments of the present invention, the illumination system further divides the beam, rotates the divided beams relatively, and then combines them into a beam traveling in the same direction again. , the excimer may be arranged in series between the laser light source 1 and the reticle (irradiated area) R to further reduce speckles. Although it is assumed that a laser is used, similar effects can be obtained using other solid-state lasers or gas lasers, and argon ion, which is a type of argon ion that originally oscillates in a narrow band, can be used instead of a narrow band laser. It can also be applied to various devices using laser light sources such as lasers.

Furthermore, the present invention is applicable not only to projection exposure type exposure apparatuses but also to proxy city and contact type exposure apparatuses.

In addition, although each embodiment of the present invention is premised on application to an exposure device, it is also possible to use a laser light source, which has similar problems, as an illumination system for observing the object surface to visualize microstructures on the object surface on a television. It can be applied in exactly the same way to alignment equipment and wafer inspection equipment that perform magnified observation using a camera or the like.

〔Effect of the invention〕

As described above, according to the present invention, the spatial coherence in the plane perpendicular to the beam traveling direction is equal in two orthogonal directions, and the image quality of the projected pattern in the vertical and horizontal directions is equal. There is an effect. That is, the two-dimensional direction (x,
Regarding y), the effect of satisfactorily reducing speckles can be obtained.

Furthermore, as described in the embodiments of the present invention, when the beams are divided and superimposed by utilizing the difference in polarization characteristics, the energy loss of the beams is reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an exposure apparatus equipped with an illumination system according to a first embodiment of the present invention, FIG. 2 is a diagram showing the beam shape at each position of the laser beam in FIG. 1, and FIG. 4 is a diagram showing the configuration of an exposure apparatus equipped with an illumination system according to a third embodiment of the present invention, and FIG. 4 is a diagram showing the beam shape at each position of the laser beam in FIG. 3. (Explanation of symbols of main parts) ■...Laser light source, 2...Beam expander, 3.6...Polarizing beam splitter-14, 5, 7
,8,9...mirror,

Claims (1)

[Scope of Claims] A light source that emits a radiation beam, and a device that transfers a pattern on an original onto an object using the radiation beam, the device being provided between the light source and the original to emit at least two radiation beams. a rotating means for rotating at least one of the divided beams around the traveling direction of the beam and converting it into a beam rotated in a direction substantially orthogonal to the other divided beam; a superimposing means for superimposing two substantially orthogonal beams, and the optical characteristics of the superimposed beams in a plane perpendicular to the optical axis are made substantially equal to each other in directions orthogonal to each other. Exposure equipment.